This invention relates generally to orthodontic treatment and more particularly to a method of applying orthodontic brackets and archwires using an ideal set up.
In orthodontic treatment, teeth are moved by the spring force of an archwire engaged in brackets attached to teeth. The more accurately orthodontic brackets are positioned on the teeth, the less the archwire must be adjusted to produce the desired tooth movement.
The most common approach today is for the orthodontist to bond the brackets upon the teeth directly in the patient's mouth, using his experience to place the bracket in a free-hand manner. Sometimes the brackets are shaped so as to assist the orthodontist's eye in placing the brackets. Often the relationships between the archwire slots and the bases of the brackets are customized for the average tooth anatomy so that the slot remains as level as possible in all planes along the arch form, i.e to avoid having to form the arch wire with first, second and third order bends. This is called the straight wire technique by A Company, a division of Johnson & Johnson, which produces brackets as disclosed in Andrews U.S. Pat. No. 4,097,993.
Sometimes, plastic positionable guides representing the long axis of the tooth and a preconceived relationship of the bracket to the initial edge are inserted into the brackets as positional guides to aid in this free hand placement.
Another method of assuring positional accuracy is to place the bracket with a temporary fixation material (e.g. caramel) onto plaster models of the teeth so that the operator can view and adjust the bracket position out of the mouth. A transfer tray is then made to place the brackets in this relationship into the mouth. This is called the indirect bonding technique.
A number of attempts have been made to cut the teeth off the plaster models and to set them in wax in an ideal position, i.e. with the model teeth repositioned in an ideal arch form. In this process, the upper and lower model teeth are accurately articulated together according to the experience of the person setting the teeth. This is similar to the way plastic teeth are set up in preparation for making full dentures. The brackets are then placed on the teeth in a level position. This method is known as the ideal setup technique, of which a number of variations are known.
Archwires may then be made using the slots of the brackets as a guide. The problem that arises here is the difficulty of shaping archwires without disturbing the positions of the brackets that are temporarily attached to the model teeth. Either clumsy mechanical fixation is necessary or time-consuming care must be used not to dislodge the brackets from the teeth.
Some means must be provided to transfer the individual brackets back to the model of the present malocclusion of the patient's teeth so that indirect trays can then be made. An alternative method is to provide an accurate enough relationship between the bracket and the individual tooth so direct transfer could be made. Dellinger U.S. Pat. No. 4,360,341 discloses an individual tooth transfer fixture which encloses the bracket and tooth in a predetermined relationship. The combination of applying bonding material along with a burnished pad and index tabs is described in Wildman's U.S. Pat. No. 4,494,931.
One of the problems in this ideal set up arrangement is the lack of experienced operators to set up a large volume of cases. Another problem is the difficulty of communication between the lab technician and the orthodontist. Orthodontists do not wish to give up control of the placement of teeth to laboratory technicians. A third problem is the difficulty of designing a machine to place the brackets properly in a level position on the teeth when the arch form varies in each case in a curved manner. These drawbacks, and others mentioned above, particularly forming the arch wire, are exacerbated when shifting from labial to lingual orthodontics.
Accordingly, a need remains for a simpler, easier-to-use method for positioning orthodontic brackets in an ideal position and producing archwires with an ideal arch form.